code: def on_postprocess_trajectory(
      self,
      *,
      worker,
      episode,
      agent_id,
      policy_id,
      policies,
      postprocessed_batch,
      original_batches,
      **kwargs,
  ):
      pos = np.argmax(postprocessed_batch["obs"], -1)
      x, y = pos % 8, pos // 8
      self.deltas.extend((x**2 + y**2) ** 0.5)
  
imports: from collections import deque
  import gymnasium
  import minigrid
  import numpy
  import sys
  import unittest
  import ray
  from ray import air, tune
  from ray.rllib.algorithms.callbacks import DefaultCallbacks
  import ray.rllib.algorithms.ppo
  from ray.rllib.utils.test_utils import check_learning_achieved, framework_iterator
  from ray.rllib.utils.numpy import one_hot
  from ray.tune import register_env
label_desc: Use image node_id 2 for calling the MyCallBack obj's underlying member method code with example usage: obj.on_postprocess_trajectory() without return types